Applet & graphics programming

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Applet
 Applet is a special type of program that is embedded in
the webpage to generate the dynamic content.
 It runs inside the browser and works at client side.
 It works at client side so less response time.
 Secured.
 It can be executed by browsers running under many
platforms, including Linux, Windows, Mac Os etc.
 Plug-in is required at client browser to execute applet.

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Applets
 Applets don’t use the main() method, but when they
are load, automatically call certain methods (init,
start, paint, stop, destroy).
 They are embedded inside a web page and executed in
browsers.
 They cannot read from or write to the files on local
computer.
 They cannot communicate with other servers on the
network.
 They cannot run any programs from the local computer.
 They are restricted from using libraries from other
languages.

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How to run an Applet?
 There are two ways to run an applet
 By appletViewer tool

By html file.

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By Appletviewer
import java.applet.*;
import java.awt.*;
/*<applet code="helloA" width=200 height=500> </applet>*/
public class helloA extends Applet
{
public void paint(Graphics g)
{
g.setColor(Color.red);
g.drawString("Hello....",10,25);
}
}
Javac helloA.java
appletviewer helloA.java

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By HTML File
<html>
<applet code="helloA.class" width=200 height=500>
</applet>
</html>

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Applet Life Cycle

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1. Initialization state
 Applet enter in initialize state when it is loaded.
 In this state called init() method & overrode the code.
 This state occurs only ones in applet life cycle.
 In this state we done following task.
 Creating Object
 Load image or font
 Set text or background Color
 Setup initials values

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2. Running state
 Applet enter the running state when the system
call the start() method of applet class.
 This state occurs automatically after the
applet is initialization.
 Starting can also occur if the applet is already
in “stopped” state.
 We may override the start() method to execute
the statement.

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3. Idle or Stopped state
 Applet become idle when it is stopped from
running.
 stopping occur automatically when we leave
the current page.
 we may override the stop() method to execute
the statement.

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4. Dead State
 Applet said to be dead when it is removed
from memory.
 This state called destroy() automatically
when we quite from a browser.
 This state occurs only once in applet life
cycle.
 This state is used to clean up resources.

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5. Display State
 Applet moves to the display state whenever is
has perform some output operation on screen.
 This happens immediately after the applet enter
in to running state.
 Almost every applet will have a paint()
method.
 We must Remember Display state is not part
of Applet life cycle.

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Graphics Class
 A Graphics object encapsulates a set of
methods that can perform graphics output.
 Specifically, it allows you to draw lines, ovals,
rectangles, strings, images, characters, and
arcs.

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Graphics class Methods

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Displaying Text
 We have seen that drawstring() method of the
Graphics class is used to display text.
 We can also display strings by using different
fonts. This is necessary in many applets.
 For example, tables and graphs use various
fonts for titles, axes, data and other
information.

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java.awt.Font
 A font determines the size and appearance of
characters in a string. Information about a font is
encapsulated by the java.awt.Font class.
 The following is one of its constructors:
 Font (String name, int style, int ps)
 Here, name identifies the font.
 Some commonly used font names are Serif,
SansSerif, and Monospaced.
 The style may be BOLD, ITALIC, or PLAIN.
 The point size of the font is ps.

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 After a font has been created, you may then use it in a
graphics context.
 This is done by calling the setFont() method of the
Grahics class.
 This method has the following format:
 Void setFont (Font font)
 Here, font is a Font object. after this method is called,
any strings that are output via the drawstring() method
are displayed with that font.
 For example:
 g.setFont(new Font("serif",Font.BOLD,36));
 g.setColor(Color.black);
 g.drawString("Font example",5,100);

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Applet Tag
 The applet viewer uses the HTML source
code at the beginning of a .java file to display
an applet.
 It is also possible to embed an applet in a
web page.
 The complete syntax for an applet tag is
shown in the following listing.
 Optional lines are enclosed in brackets.

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<applet
[codebase=url]
Code=clsName
[alt=text]
[name=appName]
Width=wpixels
Height=hpixels
[align=alignment]
[vspace=vspixels]
[hspace=hspixels]
>
[<param name=pname1 value=value1>]
[<param name=pname2 value=value2>]
…
[<param name=pnameN value=valueN>]</applet>

Applet &amp; graphics programming

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